The correct option is Project startup and scoping.

This phase is where the authorization perimeter should be defined because it establishes the system boundaries, the assets that need protection, the stakeholders and the regulatory and business requirements that drive access control decisions and security goals. Defining the perimeter during startup and scoping ensures that architecture, threat modeling and requirements capture include who and what need access and it reduces cost and rework later in the lifecycle.

Operations and maintenance is incorrect because this phase focuses on running and supporting the system after it is built and deployed. Controls can be adjusted in operations, but the core authorization perimeter must already be set to guide deployment and design choices.

Development and unit testing is incorrect because this phase is for implementing and verifying features within an already defined boundary. Defining the perimeter only at this stage risks architectural rework and missed requirements for access control and auditability.

Deployment and rollout is incorrect because this phase implements design and configuration choices that should follow from earlier scoping. Waiting until rollout to define the perimeter makes changes costly and can lead to insecure defaults during testing and operations.

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